1. Field of the Invention
The present invention relates generally to a mechanical pulley lagging used on belt conveyors for the purpose of improving drive pulley traction and increasing pulley lagging wear life.
2. Description of the Prior Art
It can be appreciated that pulley coverings have been used for many years for the purpose of improving pulley to belt traction and wear protection. The most common covering has been lagging with a rubber or other polymer covering, which is applied to the pulley outside diameter. For higher performance, other materials, such as ceramic, are used.
Ceramics have demonstrated much higher traction and wear performance. The challenge with ceramic has been in excessive conveyor belt wear and difficulty in creating and keeping the ceramic attached to the pulley. Many variants of ceramic, metal and polymer combinations have been used in various dimensional schemes. Methods of pulley attachment have also been quite diverse with gluing, welding, bolting and revulcanizing common.
Older ceramic pulley laggings use coarse ceramic materials molded to a steel backing. The steel backing is shaped to match the pulley periphery and is separated into two or three circumferential sections. These sections are then bolted, welded or glued to the pulley periphery. These products are successful at improving pulley wear and traction characteristics. They tend to fall short due to a tendency for aggressive belt wear and installation difficulty from close tolerances.
Developments using smooth dimpled ceramic tiles have reduced belt wear while retaining the improved pulley wear and traction characteristics. Approximately 1 mm dimples on the ceramic tile indent into the belt's rubber cover, creating a mechanical “gear” type link. This link results in effectively high “friction” equivalents. Geometric variances in pulley or belt and tension changes from power transfer generate varying shear forces throughout the contact surface. Locally high shear forces are inevitable and the smooth ceramic surface minimizes belt abrasion if local slips occur. This concept is currently state of the art, although it should be noted the belt wear improvement can be negated by introduction of an abrasive contaminate or a global slip between pulley and belt.
Ceramic tiles are currently attached to pulleys in these ways.                Directly bonding the tiles to the pulley periphery.        Molding the tiles into a rubber strip with metal backing and bonding, welding or retaining the strip with separate clips welded or bolted to the pulley periphery.        Placing the tiles with uncured rubber and hot vulcanizing them during the curing process.        Molding the tiles into a rubber strip and bonding the strip to the pulley periphery.        
Direct bonding of tiles to the pulley periphery has been performed successfully, although it has not achieved universal acceptance. Concerns over the rigid attachment increasing local slip and thus a higher risk of belt wear have been shown to occur. Theoretical models are emerging in the industry supporting this concern.
Tiles molded into a rubber strip and metal backing have been used successfully, typically in specific lower tension situations. Bonding of the metal backing to the pulley periphery makes it a redundant component. Bolting and welding create stress risers in the pulley complicating its design. Retaining clips have load capacity limits.
Placing the tiles with uncured rubber and creating a bond during the vulcanization process has been demonstrated in the industry. With the vast array of pulley diameters and face widths this currently uses time consuming hand tile placement and tiles tend to move as the rubber cures creating an uneven surface not ideal for some applications. Pulley size variations make use of tile positioning molds prohibitive.
The most common tile attachment is by molding tiles into a rubber strip and bonding the strip to the pulley periphery. Strip molds are rigidly designed to create a standard width, some limited length variability and provision to position ceramic tiles in a preset pattern. These standardized strips are manually bonded one by one on the pulley periphery with the width parallel to the pulley circumference and length trimmed to the pulley face width. Successive strips result in butt, or in some cases lap, joints along the face width with gaps which are then filled.
The main problem with current ceramic tile lagging is the inability to attach the tiles in a cost effective manner and consistently achieve the reliability of other rubber lagging bonds.
It is generally accepted the highest reliability bonds are those made by hot vulcanizing in an autoclave or press due to the ability to better control variables. Current ceramic tile lagging uses a press cured bond from tile to rubber and a manual bond from rubber to pulley periphery. Small bond deficiencies can grow under the stress of use and result in catastrophic bond failures. In practice, this manual rubber to pulley bond is most critical since loss of a strip will likely result in downtime to repair while the press cured tile bonds are independent and many tiles can be lost before repair is necessary. Furthermore the manual butt or lap joints between strips present a location more likely to allow liquids or debris to be pushed into the rubber to pulley bond. It will become obvious the present invention improves reliability by correcting this joint reliability mismatch.
Another deficiency of present strip designs are the butt or lap seams create a linear recessed area running the entire, or a significant portion of the pulley face width, which creates noise and vibration from the intermittent belt contact when running. In addition, for easier tile setting most designs use linear tile and groove patterns resulting in the same effect. It will become obvious the present invention eliminates this effect without additional manufacture difficulty or expense.
Another deficiency of the present strip designs is that the process of tile setting for press cure and the process of manual pulley to rubber bond are separate processes which are commonly labor intensive. In addition, present designs use very few, and many times only one, ceramic tile patterns to minimize tooling and setup costs. It will become obvious the present invention improves cost by merging these two processes into one and increases flexibility of tile layout design.
Another deficiency of the current strip designs is the need to cut and trim the strip length to match pulley face width. Most designs require the purchase of different length product for each pulley face width, which complicates logistics. Further more design variables such as rubber thickness and type of compound require different finished strips further complicating logistics. It will become evident the present invention eliminates this labor and reduces logistical complications by minimizing components required.
Furthermore, it is inconvenient and at a point impossible to install the present ceramic strip designs on small diameter pulleys due to their bending stiffness and the resulting intermittent rubber to pulley periphery contact. It will become obvious the present invention overcomes this constraint making ease of manufacture independent of pulley diameter.
In these respects, the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of creating a more cost effective and higher reliability ceramic pulley lagging.